Battle Royale, but you'll have to order it from an import company...it's not available in Region 1/US right now...
http://www.imdb.com/title/tt0266308/
In the near future in Japan, kids are uncontrollable so The Battle Royal Act is passed and every year, one class of good for nothing 9th graders gets dropped off on a deserted island with weapons and food are forced to fight to the death for 3 days until only one survivor is left...if there is more than one at the end of the 3 days, the neck collars they are wearing will explode...
The trailer:
A clip:
a reputable company you can order the DVD from...I order all my jap flicks from this place...
http://store.edaymovie.com/barodcut2d.html